Fix empty default value schema describing in sqlite.

* When getting schema for table column that omits any kind of 'DEFAULT
  ...', return populate the returned object with undefined instead of
  null so that a 'DEFAULT NULL' is not appended to subsequent CREATE
  queries.
* Fixes #5051

lib/dialects/sqlite/query.js

@@ -174,11 +174,22 @@ Query.prototype.run = function(sql, parameters) {
                   // this is the sqlite way of getting the metadata of a table
                   result = {};
 
+                  var defaultValue;
                   results.forEach(function(_result) {
+                    if (_result.dflt_value === null) {
+                      // Column schema omits any "DEFAULT ..."
+                      defaultValue = undefined;
+                    } else if (_result.dflt_value === 'NULL') {
+                      // Column schema is a "DEFAULT NULL"
+                      defaultValue = null;
+                    } else {
+                      defaultValue = _result.dflt_value;
+                    }
+
                     result[_result.name] = {
                       type: _result.type,
                       allowNull: (_result.notnull === 0),
-                      defaultValue: (_result.dflt_value === 'NULL' ? null : _result.dflt_value),
+                      defaultValue: defaultValue,
                       primaryKey : (_result.pk === 1)
                     };
 
@@ -186,10 +197,6 @@ Query.prototype.run = function(sql, parameters) {
                       result[_result.name].defaultValue = { '0': false, '1': true }[result[_result.name].defaultValue];
                     }
 
-                    if (result[_result.name].defaultValue === undefined) {
-                      result[_result.name].defaultValue = null;
-                    }
-
                     if (typeof result[_result.name].defaultValue === 'string') {
                       result[_result.name].defaultValue = result[_result.name].defaultValue.replace(/'/g, '');
                     }

test/integration/dialects/sqlite/query-generator.test.js

@@ -50,6 +50,10 @@ if (dialect === 'sqlite') {
           expectation: {id: 'INTEGER DEFAULT 0'}
         },
         {
+          arguments: [{id: {type: 'INTEGER', defaultValue: undefined}}],
+          expectation: {id: 'INTEGER'}
+        },
+        {
           arguments: [{id: {type: 'INTEGER', unique: true}}],
           expectation: {id: 'INTEGER UNIQUE'}
         },

test/integration/query-interface.test.js

@@ -182,7 +182,14 @@ describe(Support.getTestDialectTeaser('QueryInterface'), function() {
           }
           expect(username.type).to.equal(assertVal);
           expect(username.allowNull).to.be.true;
-          expect(username.defaultValue).to.be.null;
+
+          switch (dialect) {
+            case 'sqlite':
+              expect(username.defaultValue).to.be.undefined;
+              break;
+            default:
+              expect(username.defaultValue).to.be.null;
+          }
 
           switch (dialect) {
             case 'sqlite':
@@ -201,7 +208,13 @@ describe(Support.getTestDialectTeaser('QueryInterface'), function() {
           }
           expect(isAdmin.type).to.equal(assertVal);
           expect(isAdmin.allowNull).to.be.true;
-          expect(isAdmin.defaultValue).to.be.null;
+          switch (dialect) {
+            case 'sqlite':
+              expect(isAdmin.defaultValue).to.be.undefined;
+              break;
+            default:
+              expect(isAdmin.defaultValue).to.be.null;
+          }
 
           if (dialect === 'postgres' || dialect === 'postgres-native') {
             expect(enumVals.special).to.be.instanceof(Array);